Aerial cables still enjoy widespread use notwithstanding an effort to install utilities underground. Such cables may include copper transmission media, optical fiber transmission media or both. In some urban areas, overhead transmission cables which have been in use for many years now must be replaced. The existing cables in many urban areas most likely will be replaced with overhead lines inasmuch as existing ducts are full and the cost for additional buried capacity in such urban area is uneconomical.
In one installation, an aerial cable is lashed to a support strand which extends between poles. In another, which is referred to as self-supporting or figure eight cable, a support strand is enclosed by an outer plastic jacket which is integrally connected by a web to a plastic jacket which encloses a core comprising a plurality of plastic insulated conductors. The core may be undulated as shown in U.S. Pat. No. 3,207,836, which issued on Sept. 21, 1965, to prevent the transmission of tensile strain from the support strand to the core. The core is enclosed by a plastic core wrap material and a corrugated aluminum shield. Mechanical reinforcement has been provided in the prior art by enclosing the undulated core with an inner jacket. See U.S. Pat. No. 4,378,462 which issued on Mar. 29, 1983 in the names of W. S. Arnold, L. M. Borowicz, Jr. and L. M. Rackson. A corrugated steel layer, coated with a flooding compound for corrosion resistance, is formed over the inner jacket which is then covered with the outer jacket. The jacket typically is made of polyethylene.
Customers have evinced a desire to overcome some problems which are associated with cables of the kind just described. This is particularly true in those instances where extensive rehabilitation work is being planned.
One problem relates to splicing. Craftspeople do not relish the thought of having to cut through two plastic jackets in order to access the core and splice conductors. Although there are some prior art cables which include only one shield and one jacket, these cables are not sufficiently waterblocked by today's standards. For example, when a craftsperson makes a slit in a web of typical prior art self-support cables, the slit may extend into the cable jacket which allows water to enter. Clearly, candidate aerial cables must include suitable waterblocking provisions.
Also, as is well known, aerial cable must be grounded. Generally, this is accomplished by installing electrical ground continuity throughout the length of the cable. At each splice location, for example, grounding or bond clamps, as they are often called, are attached to metal components of the cable and connected by a strap wire to carry ground continuity across the splice location. Should the aerial cable include two metallic shields such as the one described hereinbefore wherein the two shields are spaced apart by a plastic inner jacket, it becomes necessary to use two bond clamps. Desirably, one bond clamp at each location should suffice.
The sought-after cable must have suitable strength characteristics. Because of the loading to which the cable may be subjected, such as ice and wind loading, for example, steps must be taken so as not to overload the conductors. Otherwise, the transmission quality may be affected, whereas if the transmission media comprise optical fibers, the fibers may break.
What is needed and what seemingly is not provided for in the prior art is an aerial cable which facilitates splicing and electrical bonding. Also, it must be one which includes suitable waterblocking provisions and which is sufficiently flexible so as not to impede installation. The sought after cable must be competitive in price with prior art offerings and be easily installed. Also desired is a cable which may include metallic conductor and/or optical fiber transmission media.